The present invention relates to a connection structure having a sealing function for connecting plugs, nozzles, terminals, connectors, and the like that have a spigot portion (hereinafter referred to as "spigot members") to socket portions of gas, pneumatic or like devices by screwing the spigot member into the socket portion. When the spigot member is tightly screwed into the socket portion, a seal flange integrally formed with the spigot member is cut off at the same time to serve as a seal packing for completely preventing leakage of gas or air.
With spigot members of the type mentioned, rubber packings are generally used for sealing. However, rubber packings are not fully satisfactory for corrosion resistance to highly corrosive gases and are, therefore, limited in application for use for a prolonged period of time.
In the field of bolts, spigot members have been proposed which are integrally provided with a washer adapted to be cut off when the spigot member is tightened up (as disclosed, for example, in Examined Japanese Patent Publication SHO 45-36689). The washer of this known spigot member is in the form of an annular flange integrally formed with the shank of a bolt under its head. The flange is spot-joined to the bolt shank at two to three portions around the shank, so that when the flange is separated off, twisted projections remain at these portions, making it impossible to hold the entire flange under uniform pressure. Moreover, the bolt portion including the flange is difficult to make by cutting, and the spigot member can not be manufactured with high precision.